Method and apparatus for controlling the concentration of a chemical solution

• US 4,733,798 A
• Filed: 02/05/1986
• Issued: 03/29/1988
• Est. Priority Date: 02/05/1986
• Status: Expired due to Term

• Current Assignee: Ecolab USA Incorporated (Ecolab, Inc.)
• Original Assignee: Ecolab, Inc.
• Inventors: Johnson, Charles B., Larson, Spencer B., Brady, Daniel F., Ziegler, David B.
• Primary Examiner(s): Rolla, Joseph J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/826,205
• Time in Patent Office: 783 Days
• Field of Search: 222/23, 222/39, 222/52, 222/54, 222/638, 222/644, 222/57, 324/441, 324/445, 137/5, 137/93, 134/113
• US Class Current: 222/23
• CPC Class Codes: A47L 15/0055 Metering or indication of used products, e.g. type or quantity of detergent, rinse aid or salt; for measuring or controlling the product concentration
• CPC Class Codes: A47L 15/241 the dishes moving in a horizontal plane
• CPC Class Codes: A47L 15/449 Metering controlling devices A47L15/4229 takes precedence
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G05D 21/02 characterised by the use of electric means
• CPC Class Codes: Y10T 137/034 Controlled by conductivity of mixture
• CPC Class Codes: Y10T 137/2509 By optical or chemical property

Abstract

The invention includes a method and apparatus for controlling the concentration of wash water in a ware washing machine. A preferred ware washing machine (10) includes a reservoir (11) for holding wash water, a normally closed valve (17) for directing clean water to a dry detergent supply (13), an electrodeless conductivity cell (12) for monitoring the conductivity of the ware washing solution, and a controller for activating the normally closed valve (15) in response to the difference between the measured concentration and the actual concentration. A preferred concentration controller includes an adjustable amplifier (48) which provides an amplified concentration signal which is equal to a reference signal when the concentration of the solution is equal to the desired concentration. In addition, a preferred conductivity cell (12) includes a thermistor (46) which, in effect, increases or decreases the voltage of the signal produced by the secondary coil to remove the apparent concentration changes solely associated with changes in temperature of the washing solution.

Claims

1. An apparatus for controlling the concentration of a detergent solution comprising:

(A) means for providing a concentration signal representing the concentration of the solution comprising a primary coil and a secondary coil, wherein when the coils are immersed in the solution the solution provides an electrical coupling between the coils;

(B) means for changing the concentration of the solution; and

(C) means for controlling the concentration changing means comprising;

(1) means for comparing the concentration signal with a reference signal representing a preselected desired concentration and generating an error signal representing the difference therebetween; and

(2) means for activitating the concentration changing means in response to the error signal, wherein the concentration changing means comprises means for increasing the concentration of the solution and wherein the activating means comprises;

(a) timing means for;

(i) continuously activating the concentration increasing means when the error signal indicates that the concentration of the solution is less than a preselected percentage of the desired concentration;

(ii) not activating the concentration increasing means when the error signal indicates that the concentration of the solution is substantially equal to the desired concentration; and

(iii) periodically activating the concentration increasing means when the error signal indicates that the concentration of the solution is between the desired concentration and the preselected percentage of the desired concentration, wherein the rate at which the concentration increasing means is activated is directly related to the difference between the actual concentration and the desired concentration, whereby overshoot is substantially eliminated; and

(b) alarm means for determining whether the concentration increasing means has been continuously activated for an excessive period of time.

2. The apparatus of claim 1, wherein the magnitude of the error signal is directly related to the difference between the concentration of the solution and the desired concentration, and wherein the timing means comprises a capacitor which is subject to charging by the error signal, wherein the concentration increasing means is not activated during the period of time that the capacitor is charging, whereby the concentration increasing means is not activated for a period of time directly dependent on the magnitude of the error signal, and is otherwise activated.

3. An apparatus for controlling the concentration of a detergent solution comprising:

(A) means for providing a concentration signal representing the concentration of the solution comprising a primary coil and a secondary coil, wherein when the coils are immersed in the solution the solution provides an electrical coupling between the coils;

(B) means for changing the concentration of the solution; and

(C) means for controlling the concentration changing means comprising;

(1) means for comparing the concentration signal with a reference signal, the reference signal comprising a first reference signal representing 100 percent of a desired concentration and a second reference signal representing a preselected lower percentage of the same desired concentration, and generating an error signal representing the difference therebetween; and

(2) means for activating the concentration changing means in response to the error signal, wherein the comparing means comprises first and second comparators, wherein;

(a) the first comparator compares the concentration signal to the first reference signal and the second comparator compares the concentration signal to the second reference signal, wherein when the second comparator indicates that the measured concentration is less than the preselected lower percentage of the desired concentration, the concentration changing means is continuously activated;

(b) when the second comparator indicates that the measured conductivity is greater than the preselected lower percentage of the desired concentration but the first comparator indicates that the measured concentration is less than the desired concentration, the activating means periodically activates the concentration changing means at a rate which is directly related to the magnitude of the error signal; and

(c) when the first comparator indicates that the concentration is substantially equal to the desired concentration, the activating means does not activate the concentration changing means.

4. The apparatus of claim 3, wherein the preselected lower percentage is 90%.

5. An apparatus for controlling the concentration of a wash water solution suitable for use in a ware washing machine by controlling the flow of a concentrated solution of detergent and water to the wash water solution, comprising:

(a) means for producing a 100% reference signal representing a preselected desired wash water concentration;

(b) means for producing a 90% reference signal representing a concentration 90% of the desired concentration;

(c) means for providing an amplified temperature compensated concentration signal, comprising;

(i) a primary coil;

(ii) a secondary coil;

(iii) a thermistor operatively connected to the secondary coil for compensating for changes in the temperature of the wash water solution, wherein when the coils and the thermistor are immersed in the wash water solution, the secondary coil produces an uncompensated signal indicative of the conductivity of the wash water solution and the thermistor produces a temperature compensated concentration signal by changing the uncompensated conductivity signal in inverse relation to the temperature of the wash water solution; and

(iv) an amplifier for adjustably amplifying the temperature compensated signal to produce the amplified temperature compensated concentration signal, wherein the gain of the amplifier can be adjusted so that the amplified signal is equal to the 100% reference signal when the concentration of the wash water solution is equal to the desired concentration;

(d) a first comparator for comparing the amplified concentration signal with the 100% reference signal;

(e) a second comparator for comparing the amplified concentration signal with the 90% reference signal, wherein the comparators produce an error signal indicative of the difference between the measured ware washing solution concentration and the desired concentration;

(f) means for increasing the concentration of the wash water solution comprising a normally closed valve for controlling the flow of the concentrated solution of detergent and water to the wash water solution;

(g) means responsive to the error signal for;

(i) continuously activating the normally closed valve when the error signal indicates that the concentration of the wash water solution is less than that represented by the 90% concentration signal;

(ii) not activating the normally closed valve when the error signal indicates that the concentration of the solution is substantially equal to the desired concentration; and

(iii) periodically activating the normally closed valve when the error signal indicates that the concentration of the wash water solution is between the desired concentration and 90% of the desired concentration, wherein the rate at which the normally closed valve is activated is directly related to the difference between the actual concentration and the desired concentration, whereby overshoot is substantially eliminated; and

(h) alarm means for determining whether the normally closed valve has been continuously activated for an excessive period of time.

6. A washing apparatus comprising:

(A) means for containing a washing solution

(B) means for providing a concentration signal representing the concentration of the solution comprising a primary coil and a secondary coil, wherein when the coils are immersed in the solution the solution provides an electrical coupling between the coils;

(C) means for changing the concentration of the solution; and

(D) means for controlling the concentration changing means comprising;

(1) means for comparing the concentration signal with a reference signal representing a preselected desired concentration and generating an error signal representing the difference therebetween; and

(2) means for activating the concentration changing means in response to the error signal, wherein the concentration changing means comprises means for increasing the concentration of the solution and wherein the activating means comprises;

(a) timing means for;

(i) continuously activiating the concentration increasing means when the error signal indicates that the concentration of the solution is less than a preselected percentage of the desired concentration;

(ii) not activating the concentration increasing means when the error signal indicates that the concentration of the solution is substantially equal to the desired concentration; and

(iii) periodically activating the concentration increasing means when the error signal indicates that the concentration of the solution is between the desired concentration and the preselected percentage of the desired concentration, wherein the rate at which the concentration increasing means is activated is directly related to the difference between the actual concentration and the desired concentration, whereby overshoot is substantially eliminated;

(b) alarm means for determining whether the concentration increasing means has been continuously activated for an excessive period of time.

7. The apparatus of claim 6, wherein the magnitude of the error signal is directly related to the difference between the concentration of the solution and the desired concentration, and wherein the timing means comprises a capacitor which is subject to charging by the error signal, wherein the concentration increasing means is not activated during the period of time that the capacitor is charging, whereby the concentration increasing means is not activated for a period of time directly depending on the magnitude of the error signal, and is otherwise activated.

8. A washing apparatus comprising:

(A) means for containing a washing solution;

(B) means for providing a concentration signal representing the concentration of the solution comprising a primary coil and a secondary coil, wherein when the coils are immersed in the solution the solution provides an electrical coupling between the coils;

(C) means for changing the concentration of the solution; and

(D) means for controlling the concentration changing means comprising;

(1) means for comparing the concentration signal with a reference signal, the reference signal comprising a first reference signal representing 100 percent of a desired concentration and a second reference signal representing a preselected lower percentage of the same desired concentration, and generating an error signal representing the difference therebetween; and

(2) means for activating the concentration changing means in response to the error signal, wherein the comparing means comprises first and second comparators, wherein;

(a) the first comparator compares the concentration signal to the first reference signal and the second comparator compares the concentration signal to the second reference signal, wherein when the second comparator indicates that the measured concentration is less than the preselected lower percentage of the desired concentration, the concentration changing means is continuously activated;

(b) when the second comparator indicates that the measured conductivity is greater than the preselected lower percentage of the desired concentration but the first comparator indicates that the measured concentration is less than the desired concentration, the activating means periodically activates the concentration changing means at a rate which is directly related to the magnitude of the error signal; and

(c) when the first comparator indicates that the concentration is substantially equal to the desired concentration, the activiating means does not activate the concentration changing means.

9. The apparatus of claim 8, wherein the preselected lower percentage is 90%.

10. A ware washing apparatus comprising:

(a) a reservoir for containing the ware washing solution;

(b) means for producing a 100% reference signal representing a preselected desired wash water concentration;

(c) means for producing a 90% reference signal representing a concentration 90% of the desired concentration;

(d) means for providing an amplified temperature compensated concentration signal, comprising;

(i) a primary coil;

(ii) a secondary coil;

(iii) a thermistor operatively connected to the secondary coil for compensating for changes in the temperature of the wash water solution, wherein when the coils and the thermistor are immersed in the wash water solution, the secondary coil produces an uncompensated signal indicative of the conductivity of the wash water solution and the thermistor produces a temperature compensated concentration signal by changing the uncompensated conductivity signal in inverse relation to the temperature of the wash water solution; and

(iv) an amplifier for adjustably amplifying the temperature compensated signal to produce the amplified temperature compensated concentration signal, wherein the gain of the amplifier can be adjusted so that the amplified signal is equal to the 100% reference signal when the concentration of the wash water solution is equal to the desired concentration;

(e) a first comparator for comparing the amplified concentration signal with the 100% reference signal;

(f) a second comparator for comparing the amplified concentration signal with the 90% reference signal, wherein the comparators produce an error signal indicative of the difference between the measured ware washing solution concentration and the desired concentration;

(g) means for increasing the concentration of the wash water solution comprising a normally closed valve for controlling the flow of the concentrated solution of detergent and water to the wash water solution;

(h) means responsive to the error signal for;

(i) continuously activating the normally closed valve when the error signal indicates that the concentration of the wash water solution is less than that represented by the 90% concentration signal;

(ii) not activating the normally closed valve when the error signal indicates that the concentration of the solution is substantially equal to the desired concentration; and

(iii) periodically activating the normally closed valve when the error signal indicates that the concentration of the wash water solution is between the desired concentration and 90% of the desired concentration, wherein the rate at which the normally closed valve is activated is directly related to the difference between the actual concentration and the desired concentration, whereby overshoot is substantially eliminated; and

(i) alarm means for determining whether the normally closed valve has been continuously activated for an excessive period of time.

11. An appartus for controlling the concentration of a detergent solution comprising:

(A) means for providing a concentration signal representing the concentration of the solution comprising a primary coil and a secondary coil, wherein when the coils are immersed in the solution the solution provides an electrical coupling between the coils;

(B) means for changing the concentration of the solution; and

(C) means for controlling the concentration changing means comprising;

(1) means for comparing the concentration signal with a reference signal representing a preselected desired concentration and generating an error signal representing the difference therebetween; and

(2) means for activating the concentration changing means in response to the error signal, wherein the concentration changing means comprises means for increasing concentration of the solution and wherein the activating means comprises;

(a) timing means for;

(i) continuously activiating the concentration increasing means when the error signal indicates that the concentration of the solution is less than a preselected percentage of the desired concentration;

(ii) not activating the concentration increasing means when the error signal indicates that the concentration of the solution is substantially equal to the desired concentration; and

(iii) periodically activating the concentration increasing means when the error signal indicates that the concentration of the solution is between the desired concentration and the preselected percentage of the desired concentration, whereby overshoot is substantially eliminated; and

(b) alarm means for determining whether the concentration increasing means has been continuously activated for an excessive period of time.

12. The apparatus of claim 11, wherein the magnitude of the error signal is directly related to the difference between the concentration of the solution and the desired concentration, and wherein the timing means comprises a capacitor which is subject to charging by the error signal, wherein the concentration increasing means is not activated for a period of time directly depending on the magnitude of the error signal, and is otherwise activated.